Wireless communication systems, such as W-CDMA (Wideband Code Division Multiple Access) and CDMA2000 communication systems, which perform communication through wireless communication channels have spread worldwide. In such wireless communication systems, a plurality of radio base stations are deployed in a service area, and a radio terminal communicates with another through any of the radio base stations. In this wireless communication, adjacent radio base stations have an overlapping zone between their wireless communicable service areas so that even when the wireless communication environment worsens, signals can be handed over between the base stations.
The wireless communication method adopts code division multiplexing, time division multiplexing, frequency division multiplexing, orthogonal frequency division multiplexing, and so forth. Therefore, multiple radio terminals are usually able to connect with one radio station at the same time.
However, even within the wireless communicable service area of a radio base station, it is often difficult to perform high-speed communication in the vicinity of the area boundary because the wireless communication environment is not very satisfactory. In addition, even within the area, the propagation of radio signals is disturbed by buildings, etc., so that an insensitive zone sometimes occurs in which a satisfactory radio connection with a radio base station is difficult.
Hence, it has been proposed that relay stations (RSs) are disposed within the service area of the radio base stations so that the radio terminals and radio base stations can perform wireless communication via RSs. Particularly, in the task group of the IEEE 802.16j, the introduction of such a relay station is now being examined.
Matters on the IEEE 802.16 are disclosed, for example, in the following nonpatent documents:    Nonpatent document 1: IEEE Std 802.16-2004    Nonpatent document 2: IEEE Std 802.16e-2005